An ink jet marking method has hitherto been widely used for marking patterns, composed of characters, symbols, diagrams and figures, on workpieces such as, for example, metals, synthetic resins, ceramics, papers, and fabrics, which are manufactured in factory lines. This system is intended to carry out marking while changing relative positions of a workpiece and an ink jet nozzle by a transfer unit as disclosed, for example, in Japanese Patent Application Disclosure Gazette SHO. 57-14981, and therefore conjunctive operation of the transfer unit and the ink jet unit is essentially required.
Along with a trend in recent years of downsizing workpieces, such as semiconductor products, the marks to be used have had to become smaller with greater preciseness. Therefore, a laser marking apparatus has been used lately instead of the ink jet system. The conventional laser marking apparatus has been such that a laser beam, obtained from a laser oscillator through a polarizer, is used to raster-scan a mask surface, and the laser beam which passes through the mask is irradiated onto a workpiece.
However, in such laser marking apparatus, the laser beam which passes through the mask is polarized toward a workpiece transfer line, a workpiece is temporarily stopped when it reaches a laser irradiation area, which is fixed, and marking is performed by irradiating the laser beam onto the surface of this stationary workpiece. Therefore this system includes a problem in that the transfer line has to be stopped for marking on each workpiece, and improvement of the production time will be impaired.